Five white youths who shouted "What – what, nigger?" at Stephen Lawrence before forcing him to the ground and killing him did so for no other reason than the colour of his skin, the Old Bailey has heard.

Opening the trial against Gary Dobson, 36, and David Norris, 35, the prosecutor Mark Ellison QC on Tuesday picked out racism as the main motive for the fatal stabbing 18 years ago as the A-level student waited at a bus stop with a friend.

"The only discernible reason for the attack was the colour of his skin," Ellison told the jury.

"The way in which the attack was executed indicates that this group were a group of like-minded young, white men who acted together and reacted together.

"They shared the same racial animosity and motivation."

As Ellison began to outline the killing of Stephen Lawrence, his father Neville stood up and left the court. Doreen Lawrence and her surviving son, Stuart, remained in court.

The jury sat behind small TV screens which were used to display some of the evidence, as the prosecutor took them back to the night of 22 April 1993, when Lawrence and a friend were waiting for a bus at a stop in Well Hall Road, Eltham, London.

There was trouble with the service, Ellison said, so the two young men walked towards a roundabout to see if there was a bus coming. They did not see one and turned around and headed back to the bus stop. As they approached the zebra crossing a group of five white youths began crossing the road.

Duwayne Brooks, Lawrence's friend, said he heard one of the five shout: "What, what nigger", and at the same time the two young black men were rushed by the group. Brooks turned to Lawrence and told him to run, but the group chased them and caught them at the junction of Dickson Road and Well Hall Road. Slightly ahead of Lawrence, Brooks managed to run back to the bus stop, before turning round and shouting to his friend: "Get up and run Steve."

"Stephen Lawrence didn't manage to get away," said Ellison. "The group quickly surrounded him. One witness said he was swallowed up by the weight of their number and simply forced to the ground."

In the following seconds there were hand and leg movements and Lawrence was stabbed twice, once in the right collar bone as he was standing, a second time in the left shoulder, probably while on the ground. Both knife wounds severed arteries. The five attackers then left, heading up Dickson Road leaving Lawrence on the ground.

Despite the seriousness of his injuries he was able to pick himself up and make his way towards Brooks, the court heard.

"This group had attacked as one," said Ellison. "The stab wounds were inflicted and then they decamped as one."

Bleeding profusely, Lawrence was able to run some way up Well Hall Road. "He ran a distance of 220 yards from where he had been stabbed. There he collapsed on the pavement opposite the junction … never to get up again."

When police arrived at the scene later Lawrence's bag was found lying near a small pool of blood near where he was attacked. On the April night spring blossom had fallen and lay on top of the fresh blood when police photographs were taken.

Brooks called 999 at 10.43pm from a telephone box after Lawrence collapsed. He then hailed down passersby, including an off-duty police officer who came to his and Lawrence's aid. "They tried to make Stephen Lawrence as comfortable as they could. A rug was put over him. Police officers arrived by about 10.50pm. The ambulance crew arrived at 10.54pm but by then Stephen Lawrence was showing no sign of life."

He was pronounced dead in hospital before midnight.

The jury was told that the key to the case against Dobson and Norris was new scientific evidence which had not been available at the time of Lawrence's death. No one had ever been able to identify the youths involved in the attack – that remained true today, Ellison said.

"The evidence was discovered for the first time during a cold case review that began in 2007. Where it not for the new scientific findings it would still be the case that there would be no reliable evidence to support the prosecution of anyone."

But the new tests, carried out by a different firm of forensic scientists who specialise in reviewing old cases, had retrieved textile fibres, blood and hair linked to Lawrence on the clothing seized from the defendants when they were first arrested in connection with the murder in May 1993, the court heard.

"Our case is that the only reasonable inference to be drawn … is that material recovered from each defendants clothes 15 days after the murder indicates they must have been members of the group that attacked Stephen Lawrence that night."